This invention relates to corner structures for semi-membrane tanks of the type frequently used to hold liquids at cryogenic temperatures.
U.S. Pat. No. 5,727,492 discloses a semi-membrane tank for holding liquefied gases such as liquefied natural gas (LNG). As described in that patent the walls of semimembrane tanks consist of curved plates having horizontal edges which are welded together and are joined at their corners to a vertical cylindrical corner by hot forming the ends of the curved plates in order to obtain a square edge for welding to the edge of the vertical corner. This arrangement tends to produce high stresses at the transition between the curved plates and the vertical corner cylinder and the radical change in shape from the curved section to the square edge at the attachment point results in stress concentrations.
In the Becker et al. U.S. Pat. No. 3,314,567, the corner of a liquid storage tank is provided by a cylindrically shaped wall member extending through an approximately 90xc2x0 arc which is butt welded at each end to orthogonally oriented beam members having angular projections to which the cylindrical walls are welded. The Corvino U.S. Pat. No. 3,414,155 provides a corner for an LNG tank consisting of a vertical beam with a curved outer section and a right angle inner section to which the orthogonally extending wall members are joined. In the Bridges et al. U.S. Pat. No. 3,721,362, tank corners are provided by specially shaped transition members to which oppositely directed corrugated members in adjacent orthogonal walls are welded.
Accordingly, it is an object of the present invention to provide a vertical corner transition arrangement for semi-membrane tanks which overcomes disadvantages of the prior art.
Another object of the present invention is to provide a vertical corner transition arrangement for semi-membrane tanks which eliminates potential fatigue cracking at the interface between the curved tank wall plates and the vertical cylindrical corners and improves the overall ability to manufacture such corners.
These and other objects of the invention are attained by providing a modified extruded vertical aluminum I-beam having a center web to which the ends of horizontal curved wall sections of the tank are welded on one side and a vertical tapered stiffening corner block is welded on the opposite side so that an unstiffened vertical curved cylinder section can be butt-welded to the projecting narrow end of the stiffening corner block. With this arrangement high stresses in the corner sections are reduced and manufacture of the corner sections is facilitated since there is no need to transition curved side and end plates into a flat vertical corner plate.